1. Technical Field
The invention relates to systems and methods for illuminating and evaluating surfaces. More particularly, the invention relates to systems and methods for illuminating an object's surface with light at varying angles of incidence and intensity and for optically evaluating the object surface for features and defects. In certain specific implementations of the systems and methods, the target object comprises a coin and the systems and methods are used to accurately objectively evaluate the numismatic quality of the coin and/or identify the coin.
2. Definitions
The following terms and phrases are used herein in accordance with the following meanings:
1. Coins--collectible pieces, including metallic money, tokens, medals, medallions, rounds, etc.
2. Obverse/Reverse--obverse is the side of a coin bearing the more important legends or types; its opposite side is the reverse.
3. Circulated/Uncirculated--circulation is the act of transferring a coin from place to place or person to person in the normal course of business; the term "uncirculated" is interchangeable with "mint state" and refers to a coin which has never been circulated.
4. Detracting Marks--marks on an object which have occurred after manufacture, or unintentional marks that occurred during manufacture of the object. As used herein, detracting marks include High Angle Impact Marks and Lustre Interruption Marks. High Angle Impact Marks (HAIMs) are significant digs or scratches on the surface of the object under evaluation. The "angle" refers to the inclination of the surface of the mark with respect to the object surface. Light striking such a mark will reflect specularly from the mark at an angle markedly different than that of light striking the undisturbed surface. Lustre Interruption Marks (LIMs) principally comprise wear or abrasions on the surface of the target object. For a normal lustrous coin surface, applicants have discovered that a Lustre Interruption Mark reflects light according to Snell's laws of reflection. This interaction is distinctly different than the complex interaction caused by uninterrupted lustre described below.
5. Lustre--is the effect of microscopic, radial die marks created by the centrifugal flow of metal when the planchet is struck by the forming dies. These die marks form radially arranged tightly packed facets which reflect light in complex ways. The angle, dispersion and strength of the reflected light depends on the strength and orientation of the lustre which varies from coin to coin and varies on the surface of the coin itself.
6. Strength of Strike--refers to the sharpness of design details within an object such as a coin. A sharp strike or strong strike is one with all the details of the die are impressed clearly into the coin; a weak strike has the details lightly impressed at the time of coining.
7. Angles of incidence--as used herein refers to the direction of a controllable beam of light relative to the surface normal of an object to be illuminated and evaluated. Angles of incidence include a perpendicular component range relative to the object surface (i.e., the range of angles defined by the incident light beam relative to the surface normal) and a parallel component range relative to the object surface (i.e., the range of angles defined by the incident light beam in a plane parallel to the surface). As explained herein, both the perpendicular and parallel component ranges of the angles of light beam incidence are controllable.
3. Description of the Prior Art
Although people have been collecting coins since the days of antiquity, it is only in recent times that coin values have greatly increased. One of the main determining factors of a coin's value is its grade, i.e., the condition or state of wear of the coin. A very small difference in grade can mean a large difference in price, thus making the exact grade of a coin important, especially today.
At present, two coin grading systems are prevalent. One expresses a coin's state in words or letters, the other uses a combination of letters and numbers. In the first system, the most important terms in ascending order are: good (G); very good (VG); fine (F); very fine (VF); extremely fine (EF), (XF); about uncirculated (AU); uncirculated or mint state (MS). The second system is based on an alphanumerical scale in which 1 represents the worst possible condition of preservation of a coin and 70 represents the best possible condition. In this system, a coin in uncirculated condition or mint state is referred to or categorized as an MS60 through MS70 coin.
The monetary value of a coin does not increase linearly as the coin advances within the different levels or categories of coin grades. As much as 95% of the potential monetary value of a coin may rest in being classified as an "uncirculated" (MS60 through MS70). In fact, the difference between one or two grade levels within this class may affect the value of a coin anywhere from hundreds to thousands of dollars.
Traditionally, a main difficulty inherent in classifying a coin within one of the above categories has been in defining the categories exactly. More serious, however, has been the difficulty inherent in matching a particular test coin with one of the predefined grade categories since all grading to date has at least in part involved a subjective evaluation(s) by an appraiser or numismatist.
Known methods for defining what is meant by a particular grade category either use textual descriptions, lined drawings, photographs or facsimile coins. With each of these methods, the category to which a coin is assigned ultimately depends to a large extent upon the numismatist conducting the evaluation. For example, textual descriptions of categories are susceptible to different interpretations by different individuals. Lined drawings often do not accurately represent the characteristics of actual coins and are normally utilized only to represent one particular type of defect or imperfection. Photographs and facsimile coins are often representative of a combination of types of defects which should be considered in evaluating coins, such as a photograph or facsimile coin illustrating visible wear and numerous bag marks. Clearly, such a guide provides a difficult standard and one which is open to various interpretations, especially, e.g., should no wear be visible but bag marks are present on the coin under evaluation.
Further, even if the grading system categories are understood by an individual, most, if not all, prior art methods of evaluating coins require the numismatist to subjectively match a particular test coin with a grade category. The principal factors to an accurate prior art appraisal of a coin are the appraiser's skill and experience, the lack of which can result in a particular coin being categorized significantly different than its true grade. However, even with an experienced appraiser, a particular coin may be categorized differently based upon environmental factors such as, for example, the time of day, the presence or absence of magnification, and the type and amount of lighting applied to the surface of the coin.
The problems inherent in subjective grading methods have been highlighted and intensified by the recent expansion of the number of grade system categories being used, e.g., from the three or four previously used uncirculated categories to the eleven (MS60 through MS70) now used by some appraisers. A commonly heard complaint in the grading industry is that it is simply impossible to consistently and accurately categorize a coin with such a large number of grade levels. In response to this, at least one grading firm is requiring that each submission be evaluated by five recognized numismatists and that four of the five independently agree as to the grade category of the coin. Although such a program does result in a more accurate grading of coins, it is obviously a very costly and time consuming operation.
Another approach to addressing the subjectiveness problems of today's coin grading techniques is disclosed by Mason in U.S. Pat. No. 4,191,472. In Mason, apparatus is provided to assist an individual in evaluating some of the more important factors which influence the grade of a coin. This apparatus comprises sets of facsimile coins, for a given class or issue, representative of particular types of coin defects or imperfections. The facsimile coins within each set are arranged according to increasing or decreasing extents to which the coin defect is exhibited. Each of the facsimile coins has assigned to it a number representative of the relative value thereof based upon the extent to which the facsimile exhibits the particular coin defect. The numeric values of the facsimile coins which exhibit the defects to the same extent (roughly) as a test coin are noted and summed to arrive at a total numeric value for the coin. The monetary value or grade of the test coin is then determined with reference to tables which correlate the total numeric value of the test coin to a monetary value.
Although it is claimed in Mason that the described apparatus allows for the "objective" evaluation of coins, a subjective interpretation of the various facsimile coin definitions and matching of a test coin to a particular definition is still required. Mason simply assists the appraiser by directing his attention to some of the individual factors which comprise the various grade levels. Further, Mason only provides for consideration of selected factors such as bag marks, and coin lustre, and does not address equally important considerations such as the location of the bag marks on the surface of the coin.
An issue closely related to coin grading involves the identification of lost or stolen coins. The importance of "fingerprinting" collectable coins for future identification is also of greater importance today as the value of such coins has increased. Presently, a coin is traced and identified via stored photographs of the coin, which are typically taken at the time the coin is graded. This procedure is sufficiently accurate, yet it is very time consuming to initially record the coins and then to subsequently search through a large number of coin photographs to identify a particular coin, much too time consuming to undertake with each coin being graded, at least not without first having a suspicion that a particular coin has been previously reported as lost or stolen.
An illumination system which can efficiently and economically provide different, controllable illumination of an object under study is not limited to use with an objective coin grading system of a type described herein and in the cross-referenced case. Rather, the systems, and accompanying surface evaluation methods, presented herein are applicable to many types of vision systems such as automatic measurement techniques for precision products ranging from mechanical parts made to very narrow tolerances to minute VLSI semiconductor products. In addition, such illumination systems and methods can be employed in microscopy, microphotometry, and microphotography, where the part being examined is viewed under some substantial magnification and image enhancement. Those skilled in the optics art will recognize further uses for the systems and methods described herein.
To summarize, there presently exists a genuine need for accurate surface illumination and evaluation techniques, for example, for use in a fully objective system for categorizing a coin at an appropriate grade level and for "fingerprinting" a coin for recordation and subsequent comparison with other coins.